Therein lies the issue, though! DC tried to sell the Spirit as his own, individual property following the Batman crossover issue, and it folded after about thirty issues. This is, IMO, the major issue with a lot of new books from the Big Two, these days, that if they don't have a recognisable brand name on there then some particular properties just don't have much of a chance.
So really, it's nothing to do with DC not wanting their characters to sell, but more that some fans just aren't interested. Having an unusual version of Batman in there, though, then manages to hold some kind of appeal.